1. Field of Invention
The present invention relates to a power management circuit and a power management method, in particular to one that is capable of charging a battery while providing power to a load circuit.
2. Description of Related Art
FIG. 1 shows a schematic circuit diagram of a prior art power management circuit. As shown in FIG. 1, a switching regulator 11 receives a feedback signal related to an output voltage Vout, and converts an input voltage Vin to the output voltage Vout. The output voltage Vout is supplied to a load circuit 12, and the output voltage Vout also charges a battery 14 through a linear regulator 13. The switching regulator 11 may be, for example, a synchronous or asynchronous buck converter as shown in FIGS. 2A-2B, or a synchronous or asynchronous boost converter as shown in FIGS. 2CA-2D. The linear regulator 13 may be, for example, a circuit shown in FIG. 2E. In order to keep the output voltage Vout above a minimum voltage Vmin to meet the requirement of the load circuit 12, an output voltage detection circuit 15 is required which receives the output voltage Vout and generates a feedback signal which is sent to the switching regulator 11. The switching regulator 11 switches a power switch to convert the input voltage Vin to the output voltage Vout according to the feedback signal, while keeping the output voltage Vout above the minimum output voltage Vmin.
In this prior art, when the output voltage Vout charges the battery 14 through the linear regulator 13, if the voltage difference between the output voltage Vout and the battery voltage Vbat is too large, it may consume too much power and there would also be a heat dissipation problem. To overcome this problem, U.S. Pat. No. 7,710,079 discloses a power management circuit which controls the voltage difference between the output voltage Vout and the battery voltage Vbat. However, in the circuit proposed in U.S. Pat. No. 7,710,079, an error amplifier with three inputs is required, which compares the output voltage Vout, the battery voltage Vbat and a constant reference voltage, for controlling the voltage difference between the output voltage Vout and the battery voltage Vbat and providing a proper output voltage Vout to the load circuit 12.
To deal with the same problem of power consumption and heat dissipation, and to enhance the efficiency of power management, the present invention proposes a different approach which only requires a general error amplifier with two inputs to achieve the same function.